1. Field of the Invention
The present invention generally relates to a fuel supply apparatus for an engine, having at least a fuel injection valve for injecting fuel into the engine, a fuel tank for storing fuel, a fuel pump for discharging fuel from the fuel tank via a fuel pipe, a pressure sensor detecting a fuel pressure in the fuel pipe, a relief valve capable of returning the fuel from the fuel pipe to the fuel tank depending on the fuel pressure prevailing in the fuel pipe, and a control unit for controlling operation, and also to a control method for the fuel supply apparatus. More, particularly, the present invention relates to technique which is contrived to control the fuel pump so as to perform feedback control of discharging operation of the fuel pump when an abnormal operation state, e.g., a failure, occurs in the pressure sensor.
2. Description of the Related Art
Japanese Patent National Publication of Translated Version No. 2000-511992 discloses a fuel supply apparatus for an engine, in which a fuel pump is activated based on both a fuel pressure detected by a pressure sensor and a reference pressure, and in which, in the case where an abnormality in the pressure sensor is detected, the fuel pump is adjustably operated based on both a required engine fuel amount and an engine rotating speed.
As described in the above, in the case where the fuel pump is operated based on both the required engine fuel amount and the engine rotating speed an amount of fuel which corresponds to the amount of consumption of fuel in the engine is discharged from the fuel pump.
Therefore, in the case where a pump controlling is shifted to that based on both the required engine fuel amount and the engine rotating speed under a state where the fuel pressure is converged to the vicinity of a target fuel pressure, it is possible to maintain the fuel pressure in the vicinity of the target fuel pressure.
Nevertheless, in the case where the pump controlling is shifted to that based on both the required engine fuel amount and the engine rotating speed during a process in which the fuel pressure is increased up to the vicinity of the target fuel pressure, since the amount of fuel corresponding to the consumption amount of fuel in the engine is replenished, it is impossible to increase the fuel pressure up to the vicinity of the target fuel pressure, and further, the fuel pressure becomes inconsistent.
Accordingly, when an abnormality or a trouble occurs in the pressure sensor during the process of increasing the fuel pressure, the control accuracy of an injection amount to the engine by a fuel injection valve is significantly lowered and an air-fuel ratio becomes excessively leaner, so that, sometimes, the engine operating stability is largely degraded.